Check valves or non-return valves, which are the subject matter of the present invention, are used to preset the direction of flow of a fluid inside a pipe and to prevent the fluid being able to flow in the opposite direction to the specified one. If need be, i.e. in the event of a reversal of the flow direction (return stroke), the valve automatically prevents passage of the fluid, which may be a gas or a liquid.
The known check valves are constructed in accordance with the same basic principle, according to which namely a pivotably supported flap serves as a shut-off body, by means of which the throughflow opening surrounded by the valve seat may be closed in the event of undesirable return flow of the fluid. Check valves having a ball as a shut-off body (ball check valves) or a disk seated on a bolt as a shut-off body (disk check valves) are in principle prior art but are not the subject matter of the invention. The invention is limited to valves having a non-return flap as a shut-off body.
In the case of the latter, it is necessary in principle to distinguish between two types, namely on the one hand check valves, in which the flap is fastened to a lever that is guided by means of a shaft supported rotatably in the housing (swing check valve), and on the other hand check valves, in which the flap itself is guided by means of a shaft supported rotatably in the housing (wafer swing check valve).
The types, in which the flap is fastened to a lever that is guided by means of a shaft supported rotatably in the housing, are based on the physical operating principle of gravitational force, i.e. the overall effect of the torques produced as a result of the inertial forces of the flap module (lever, flap, add-on pieces) is that the flap in every intended installation position of the valve is pressed against the seat face or valve seat and the valve is closed. In this case, the closing function is assisted by the pressure difference that is produced in the line system by the pressure drop caused by the return flow of the fluid. For the total of all the torques to be oriented in the direction of the seat face, the axis of rotation of the shaft has to occupy a specific position and possess a minimum clearance relative to the seat face. As a result of this, the geometry of the lever is preset and defined. In the actual background art, the levers are cast in an L-shape and then cut. Manufacture is relatively complex and cost-intensive. A cast lever requires a minimum wall thickness, with the result that its mass and, by extension, the centre of gravity are disadvantageously shifted towards the axis of rotation. This shift has to be absorbed by means of additional compensating weights. This additionally increases the cost of the components. Furthermore, the cast levers are generally screw-connected to the shut-off body. For this type of connection, because of the mechanical loads of this type of check valve during operation, it is absolutely essential to introduce a screw locking device. This markedly increases the mounting outlay for the flap module.
In the other types of check valve, in which the flap itself is guided by means of a shaft supported rotatably in the housing, the axis of rotation lies level with the seat face or valve seat. By virtue of this arrangement, the generation of an adequate torque in the direction of the seat face for all installation positions between a horizontal and a vertical alignment is virtually ruled out. These types therefore use additional mechanical springs to press the flap in every intended installation position of the valve with adequate spring tension against the seat face and to close the valve. Here too, the closing function is assisted by the pressure difference that is produced in the line system by the pressure drop caused by the return flow of the medium.
The previously described types of check valve have several drawbacks. These include the fact that the shut-off bodies often project into the flow path and therefore have a negative influence on the flow behaviour. The mounting of the flap modules is also difficult because they have to be mounted in a relatively small space between two connecting pieces. If the valve itself is supported rotatably, a very precise alignment of the axis of rotation relative to the seat face is necessary, this in turn calls for very precise manufacturing tolerances and leads to correspondingly high manufacturing costs. In many types, it is also no longer a straightforward matter to exchange the shut-off body once the valve has been assembled. Finally, a serious drawback of the types, in which the flap module comprises a lever, is the complex construction of the flap module and the increased mounting outlay occasioned thereby.
The object of the present invention is therefore to provide a check valve that is easier to manufacture.